This invention relates to the control of fuel injection in a direct injected, multi-cylinder internal combustion engine, and more particularly, to a method of interrupting the injection of fuel into a varying portion of engine cylinders, during a transition associated with a deceleration fuel cut-off mode of engine operation.
Conventionally, the supply of fuel to all cylinders of an internal combustion engine is completely interrupted during a mode of engine operation commonly known as deceleration fuel cut-off (DFCO). Entry into the DFCO mode is customarily initiated when the engine is decelerating, with the engine control element (typically the throttle valve or accelerator pedal) positioned for engine idling The purpose of this mode of operation is to reduce fuel consumption and maximize engine braking induced by the drag, or negative torque applied by the engine load Recovery from the DFCO mode is generally initiated, when either the engine rotational speed drops below a predetermined minimum speed near idle, or the engine control element is moved from the idling position to accelerate engine rotation and increase output torque.
If an engine is quickly transferred from normal operation, to the deceleration fuel cut-off mode, or vice versa, the sudden transition in engine output torque from positive to negative, or negative to positive, results in undesirable ringing or jerking in the engine driveline. These torque transients are particularly noticeable, when a manual transmission is used in coupling the driveline to the engine.
According to conventional practice, the output torque transients are smoothed by gradually adjusting engine spark timing or the quantity of fuel injected into an engine, during entry into and recovery from the DFCO operating mode. Both of these traditional approaches have a negative impact on engine exhaust emissions, because they substantially increase the amount of hydrocarbons present in the engine exhaust.
Consequently, there exists a need for a method of controlling an internal combustion engine during entry and recovery from deceleration fuel cut-off, to provide smooth transitions between negative and positive engine output torque, without substantially increasing engine exhaust emissions.